A basic structure for an organic light-emitting diode (OLED) was mentioned by Tang et al. (Appl. Phys. Lett. 51, pages 913 ff., 1987). Current structures for organic light-emitting diodes are mainly always based on the same principle. A stack of layers is formed on a substrate, where an arrangement of layers, usually exhibiting a total thickness of about 100 nm, is formed between an electrode and a counter electrode with organic layers. An anode and a cathode, which can be used to operate the organic light-emitting diode subjected to electrical voltage and through which the component emits light, are formed with the electrode and the counter electrode. A so-called hole transportation layer, made from an organic material, is usually arranged near to the anode in the arrangement of layers. A so-called electron transportation layer, produced from an organic material, is arranged near to the cathode. The charge carriers, in fact electrons and holes, injected into the arrangement of layers at the application of electrical voltage, are transported to a light-emitting area, also formed as a layer, and recombine there when light is emitted.
DC voltage is usually applied during operation, to make the organic light-emitting component produce light. Components of this type that are operated with DC voltage demonstrate certain limitations. The charge carriers are injected into the arrangement of organic layers, which is formed as an organic film, for example, at the application of electrical voltage at the electrodes, in such organic light-emitting diodes. Special electrode materials are necessary to guarantee a good injection of electrons and hole from the electrodes. A good injection means that only a slight decline in voltage arises in the area of the transition between the electrodes and the arrangement of organic layers. A treatment of electrodes with oxygenated plasma or a UV-ozone treatment can be provided; this usually brings advantages in the case of a basic electrode made of ITO (indium tin oxide).
The electrical field is always formed in the same direction, to create electronic luminescence, in organic light-emitting diodes that are operated with DC voltage. The consequence of this is that a stationary force is exerted on all the charge carriers in the electrical field. The constantly demodulated forces lead to the migration of particles or small parts in the arrangement of layers made from organic material under certain circumstances, particularly if they are charged electrically; this limits the useful life of the component.
Organic light-emitting diodes are so-called surface emitters, with at least one of the electrodes being (semi-)transparent, in order to decouple the light created from organic material in the arrangement of layers. At least the (semi-)transparent electrodes are usually formed as a very thin layer for this reason. These electrodes exhibit a small cross section of the flow of the current, through which losses arise, during the operation of the component. These losses of resistances in the electrode are significant in the case of components with a large surface, such as display screens or flat lighting units.
Stacked architectures, where a plurality of organic light-emitting diodes are stacked over each other and connected by electricity, are known as a type of construction of organic light-emitting components for DC voltage operation in addition (EP 1 804 308, EP 1 804 309). The stacked architecture has at least two advantages over individual organic light-emitting diodes. Firstly, the stacking of a plurality of organic light-emitting diodes means a corresponding multiplication of the quantity of light. Apart from this, operating stability can be increased, if the stacked organic light-emitting diodes are operated with a lower operational voltage, during which the light quantity of an individual diode is always still achievable.
The individual units are usually connected by means of different inorganic materials, which serve as a charge carrier generation layer, in stacked architectures of organic light-emitting diodes operated with DC voltage (compare Canzler et al., Proc. of SPIE, Vol. 6333, pages 11 ff., 2006; Gu et al., J. Appl. Phys. 86, pp. 4076 ff., 1999; Matsumoto et al., SID 03 Digest, pp. 979 ff, 2003; Kanno et al., Adv. Mat. 18, pp. 339 ff., 2006; Sun et al., Appl. Phys. Lett. 87, pp. 093504 ff., 2005). Stacked architectures in which a pn-transition (or pn-layer transition) is arranged between two organic light-emitting diodes stacked over each other, where an n-doped layer is formed using an alkali metal and a p-doped layer is formed using FeCl3, have been suggested apart from this (Liao et al., Appl. Phys. Lett. 84, pages 167 ff., 2004). Furthermore, molecular doping has been suggested for stacked components for operation with DC voltage (Canzler et al., Proc. of SPIE Vol. 6333, pp. 11 ff., 2006). The combined deposit of a matrix material and an allocated doping material to develop the doped layer, where a charge transfer, through which a doped layer with improved electricity conductivity arises for the charge carrier, takes place during the creation of the layer between the matrix material and the doping material, is characteristic of the creation of p or n-doped organic layers by means of molecular doping.
Organic light-emitting components, particularly organic light-emitting diodes that are operated with AC voltage applied to electrodes, are known in addition. The component elements provided for operation by AC voltage are based on a fundamentally different structure; different demands and requirements of the constructive assembly arise for this reason. The arrangement of layers is made of organic material arranged between the two electrodes and insulated from them, in the case of organic light-emitting components operated with AC voltage, in contrast to organic light-emitting components operated with DC current. An injection of charge carriers, from the electrodes to the arrangement of layers, should not and cannot take place. On the contrary, the charge carriers are created in the arrangement of layers itself, if electrical AC voltage is applied at the electrodes.
An organic, electronic luminescent component for operation with AC voltage is known from the US 2004/0027059 A1 document. A bipolar charge carrier generation layer, in which the charge carriers, namely electrons and holes, are created at the application of AC voltage, is arranged between each of the neighbouring light-emitting layers formed between the electrodes in the arrangement of layers, in the case of the known component. Then, the charge carriers created enter into the neighbouring light-emitting layers from the bipolar charge carrier generation layer, in order to recombine during the output of light. A similar structure is known in Tsutsui et al. (Appl. Phys. Lett. 85, Nr. 12, pp. 2382 ff, 2004). The bipolar charge carrier generation layer can be structured as one or a plurality of layers.
From the US 2005/0156197 A1 document, organic semiconductor elements for DC voltage operation are known, with a charge carrier generation layer with a pn layer transition being formed between a layer made of an organic acceptor material and one made of organic donor material.
In addition, a bipolar charge carrier generation layer is known from Terai et al. (‘Electric-field-assisted bipolar charge generation from internal charge separation zone composed of doped organic bilayer’, Appl. Phys. Lett., Vol. 90, No. 8, 21. February 2007, pp. 83502-83502).